1. Field
The present application generally relates to data storage systems, and, in particular, to a data storage system for storing data in different types of data storage media.
2. Related Art
Data can be stored in various types of storage media in different formats. For example, in a conventional format for storing data on a hard disk, the surface of a hard disk platter is divided into a number of tracks and sectors. A track corresponds to a single circular portion of the platter. A sector corresponds to a portion of a track. The data to be stored on the hard disk is divided into pieces such that a single piece can be stored within a single sector. The logical connection between the pieces of the data and the corresponding disk sectors is maintained in a directory. However, over time, as the data is repeatedly read, modified and written to the hard disk, the sectors corresponding to a single file can become scattered over the hard disk. This effect is commonly known as fragmentation, which can produce data access delays.
In a conventional format for storing data on magnetic tape, data is written serially in tracks on the tape. New data or files are appended at the end of previously written data or files, but not elsewhere. This leads to data storage inefficiency and data modification limitations.
Moreover, data may be stored in and transferred among different storage devices, such as a disk drive and a tape drive, depending on factors such as the access history of the data. For example, frequently accessed files may be kept on disk, whereas less frequently used files may be moved from disk to tape, which has a slower access time. In this manner, the disk acts as a cache with respect to the tape.
As described above, however, data is stored on tape in a format different from that of data stored on disk. For example, in conventional systems the host operating system uses a directory to locate the fragmented pieces on disk comprising a file. The host reassembles the pieces into file format before providing the data to a tape drive or before transferring the data over a network to another host where the data would again be reformatted by a storage drive attached to that host for storage according to the formatting requirements of the storage drive. All these operations, of course, add to the time it takes for data to be transferred among storage devices attached to the same host or for a host to access data associated with another host, and wastes valuable host processing and network resources.